Telephone system



May 21, 1929. M. B. sTAz'AK 1,713,564

TELEPHONE SYS'TEM Fileduune 3, -1926 2 sheets-sheet v1 May 21, 1929.

M. B.- sTAzAK 1,713,564

TELEPHONE SYSTEM Filed June 3, 1926 z sheets-sheet 2 fr V Patented May 2l, 1929.

MICHAEL B. STAZAX, OF CHICAGO, ILLINOIS, ASSIGNOR TO VXELLOGG SWITCHBOAD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS;

. Fig., 1 illustrates a complete telephone sys-V i 1,713,564 PATENT oFFlcE.

TELEPHONE SYSTEM.

, Application Afiled .Tune 3,

My invention relates to tele hone'systems' and has to do more particular y Vwith atwo Way trunk circuit used in connection with al so called private branch exchange system` 1n which-a call may be extended `from the main exchange to the private lbranch exchange and in turn extended to a substation terminating thereat by means of said trunk circuit.

A feature of my invention is theprovision of means in the trunk circuit Which actuates to disconnect the portion of the trunk terminating at the main exchange from the trunk at the branch exchangeso as to preventy the subscriber at said branch exchange froml extending a recall to the main exchange before the branch exchange operator has disconnected the trunk from the line of the branch substation.V v 7 Another feature of my invention is kthe provision of means in the trunkcircuit which permits the main exchange operator to ring on the trunk and light the trunk line lamp after thedisconnect signal has been given tothe trunk operator and before she hasrei `nl O'ved the trunk plug from the jack of the called line. Y Y

For a more complete understanding of` my invention, reference may be had to the accompanying drawings comprising Figs. and 2 which illustrate my invention operating in connection with a suitable r.telephone system Ain which Fig. 2 when placed Yto the right of teni for establishing' a connection from a calling substation at a'main exchange to a called substation terminating at a private branch exchange. 4

Referring now to F 1; to the Yleft of the drawing I illustrate a common battery substation A terminatinginto a line'cir'cuit-'L `.at a vmain exchange which comprises a line Yrelay LR, a line signal S, a cut oli' relay `CO and multiple jacks Y n A cord circuit C comprises an answering vplug AP and a calling plug CP connectedV 'by the heavily marked conductors having the condenscrs K and K2 interposed. A sleeve relay vSL .is associated wlth the answering end as is also a supervisory relay SR vvhlch control the lighting ofan answering supervi-V sory lamp AS.` The calling end of the cord circuit @comprises la'sleeve relay SL and .a Vsu'pervisory relay' SR which cont-rolthe lightingV of a Gallino'v supervisory lampY CS. A listening key 'L is provided for con- 1926. Serial No. 113,353.

nectingwtheoperators set O to the cord conj ductors of the cord circuitrC. A ringing key RK is provided for the calling` end of thecord circuit which when actuated connects the'r'inging generator G to a ply ringing `current to a v called line terminating at the same exchange o'r to slgnal a trunk operator located at a private branch exchange. A trunk jack TJ lo# cated at the main exchange is connected 'b conductors 13 and 19 to the trunk circuit 65 `1llustrated in Fig.'2 which is vlocated at the private branch exchange.: Acut'o' relay CO is associated with the trunk jack TJ as is also a line relay LR', said line relay LRV controlling the lighting of the line signal S77. Y l

The trunk circuit D located at the private branch exchange is illustrated in Fig. 2 and comprises a yringing-relay RRfwhich is en# ergized by ringing current'from the main exchange to control .theV lighting of the trunk Y branch exchange PB.

A listening key Lxfisf provided which when actuated connects `the operators set O to the trunk circuit Dthrough instrumentali` ties in the trunk D which will be more Vfully hereinafter described. A sleeve relay SL2 85 in the trunk circuit D is operated when a trunk plug'TP is connected to the jack of a called lineat the branch exchange and a link disconnect relay LD, a ringingrelay RR and a. release key RE are- 'also associatediwith 9o v the trunk D for purposes as will hereinafter be described.l Y f ,.To the right of Fig. 2 I illustrate a private branch substation 4E terminating in aline i circuit L Vat the private branch exchange `975V which comprises a line relay'LR-, a line signal S2, a cuto 'relayecCOg and a jack J Y.

Having described in general the apparatus' of Figs. 1 and 2 I will now described in-detail the Yoperation of the circuit illustrated in the Y drawings when a call is extended fromthe calling substation A at the main exchange to lthe called substation EV terminating at the private branch exchangeD. i

thraagjh the wndinfgpf the relay LR normal no" Assuming now that the subscriber at subl "la contact 2 of the cut oli" relay CO through the closed contacts of the substation switchhoolr back to ground at normal contact 3 ot cut otl relayrCO'. :The line relay LR upon energi- VZationv closes its alternate Contact 4' Aestablishing a circuit for the vline signal S, traced from battery through the lampl S tov ground atalternate contact 4 of relay LR. The operator of the cord circuit V(l noting the lighted line signal S inserts the answering ,plug AP into the jack J ot thecalling line establisliing a series energizing *circuit tor the cut ott relay CO of the line circuit Land the sleeve relayl SL ofthe cordcircuit C,

i traced from battery through the Winding of thevsleeve relay SL, coi'iductor 5, sleeve contacts of the connected plugilrl) and ack J to groundv through vthe winding ot the cut ott' re- -rcla N005 associated with the trunk 1'ack Til t Y Y .le

lay'CO.V The relay CO upon energization Vopens its normal contacts 2 and 3 to allow relayV LR todeenergize andy the opening of its alternate contact lettaces the line signal S. The insertion ot the answering plug A? into A' the jack ,l also establishes an energizing cir-v cuit orthe supervisory relay Slt of cord C traced troni battery, through `the lower winding 'of 'the vrelay SR, ring contacts oit. theV connected plug Al.) and jack J, alternate contact 2fot the relay CO, the closed contacts of the Vsivitchhoolr lat the substation A hach "through alternate contact 3 of relay CO, tip Ycontacts of the Jack Lrplug Al) to ground through the upperfwinding oit the relay'SR. vThe relay Slt upon energization opens its normal' contact 7 to prevent the preniaturc lighting of the answering supervisorylamp.

,"lhe'opeiattu' now actuates the listening hey LK which connects the opcratoi"s setl O tothe cord conductors andv she may nouv in"- quire` the Wants ot the lcalling` subscriber at substationir. Assun'iing that it is the subscriber at substation'L1 which terminates at the private.branch exchange i B, theoper'- y atoratl the niaiirexclninge Mld inserts the calling plug Cl) ofthe cord .G into the trunk piel;

Trl oit the trunk D which tcriniinirtes atvthe main exchange ME-wvl'nch o l)eration closes si circuit for the' sleeve retraced freni hattei'yjthrough the Winding the relay SL', slecveconta'ots of the connected plu andtrunk jack TU* to `round through the Winding ot the cut o'relay Cty-. The sleeve relay SL upon energization closes its alternate contact 8 vivl -ch closes a circuit for the Galline',supervisory lainp CStraced from battery tl'irough thelainp CS,- nornial conl tact 9 koiI supervisoi'y'relay SR to ground at alternate vcontact-S ot' relay SL. The cut ott relay/'CO' of the trunk circuit D upon VVenergiz'ation opens its. normal vcontacts 10 and l1 which prevents the energization Vet the relay of. the vtrunk D` and prevents lighting'oic the signal S andthe calling supervisory lainpCS of the cord C remains lighted until the'operator'actuates the ringn ing l'ey RK and returns the saine to normal.

rlhe operator at cord circuit- C new actuates 1 `the ringing key Rlwhich vconnects ringing .ot the trunk D, conductor 15, normal Contact lootrelay 17 ,conductor 18 trunk conductor 1Q, the ring contacts ol tie connected trunk Jack .TJ and plug CP to ground at 'alternate contact20 ol' the ringii'ig key Eli.

The ringing relay RR upon energization at tracts itsarniature 22 which allows its alter nate contact 23 to drop down vwhich closes Vthe circuit 'for the calling trunk lamp CL, traced from battery through the lainp, conductor to ground at alternate contact23 ot the relay BR. VThe* calling lamp CL remains lighted.` after the relay RR deenergizes because oi" the locking device which prevents the return oit' the arn'iature 22'to Vits normalV position.V The operator at the private branch exchange PB noting theV lighted calling lamp signal CL actuates her listening key LK thus connecting the operators set Q to the trunk conductors 13and 19 which of course tali-es place after the relay 17 is energized as will now be describec .Y l i Y.

Y Atte:` `i'inging current has` been applied troni the cord C at the inain exchange ME relay RR `deenergizesand after theflistening key LK has been. actuated an energizing circuit .tor .the relay 17 is established, traced f from battery, through the Winding of the relay, l17,conductor`25`, normal contact- 26 ot relay RR, conduct-or 27 to ground at alternate cont-act 28 oit the listening key LK', rl he relay 17 upon energizaticn closes its alternate contacts 29 and lrjyvhich'noiv connects theoperatous setAG to the conductors 13 'and 19 ot theftrunl D from alternate contacts 31 andt ofthe listening'lrey LK V- tact 23 oit relay RRto etlace the call lamp sige,

nal CAL and the openingof its normal contact ,37 prevents the prematureV lighting of the supervisory signal SS. Y Y

After' the operator at cord circuit C has applied ringing currentto the trunk circuit D from the generator G- she releases the ringing key RK and the closing of the normal coniio tacts of the ringing keyRK establishes a series energizing circuit forV the supervisory relay SR of cord C andthe relay V4() Vof the trunk circuit D traced `from battery through the lower winding of the relay SR', normal Acontact k of the ringing ke' RK, ring contacts ofthe connected plug C and trunk jack TJ, normal contact-41 of the 'relay'LDof the trunk circuit D, conductors 36V and. 42, through the winding of the relay yV conductoi-'43, alternate contact 44 of the listening' key LK, V'conductor 45, normal contact 46 of relay LD, trunk conductor 13, tip contacts of the connected plug CP and'trunkjack TJ ,Y normal contact 12 of ringing keyrRK to ground through theupperwinding of the relay SR ofthe cord circuit C. u The operator having inserted. the trunk vplug TPinto the jack J of the wantedprivate branch exchangesubscriber at E as before described,now restores her listening key Y held momentarily energized until thenornial contact 29 of the relay 17r closes, at which time relay 40 establishes a locking circuit for f itself through its alternate' contact 50 by current flowing from battery thru the winding of relay 40 as previously described, its alternate contact 50, .conductor 51, normal Contact 52 of the release key RE,`c0nductor 53, normal contact 29 of relay 17, conductor-.33, the trunk conductor 13, tip contacts `of connected plug CPand jack TJ to ground through the upper winding of the relay SR. The relay SR of cord circuit C is held energized over this circuit and the opening Aof its norinal contact 9` efaces the calling supervisory signal CS and notifies the operator at cord .C that the pritrunk D has answered the call.`

The insertion of the trunk plug TP into thejack J of the wanted line establishes an Aenergizing circuit for the sleeve relaySLzfof the trunk circuit D traced from battery through the winding of the relay SL2, conductor 55, sleeve contacts vof the connected plugV TP and jack J to ground through the winding ot' the cut off relay COzof theflinecirc'uit L associated with the calledprivate branch substation E. VRelay. CO2 upon energization opensI its normal contacts 56 and57 to connect the subscribers set at substation E to trunk'circuit D. The relay SL'-I upon'ene'rgization establishes a circuitrfor the supervisory signa-l SS ofthe trunk D traced from battery through the lamp SS, normal contact 37 oi relay 17,'-conductor 58 to ground at alternate contact 59 of the sleeve relay vSL2, and 'the supervisory signal SS is lighted over this circuit and remains invthis condition until the called subscriber at. E answers, Theopeiator now depress-les' the ringing key RK ofthe trunk D and connects ringing'current from the generator G to the -calledvline E traced from the generator G', alternate contact 60 of the ringing keyRK, tip contaetsof theconnected trunk plug-TP and jack J, alternate contact 56 of the cut olf relay CO2 through the condenser and call bell at the substation E back I -through alternate contact 57 of the cut off rclay CO2, the ring-,contacts ofthe connected jack J and trunk plug TP to groundlat aljternate contactfl of the ringing-key RK The subscriber-at the 'substation E,r in refov spouse to the call signal removes his receiver from the switchhook thus establishing an energizing circuit `for the supervisory relay SR2 of trunk D traced frornbattery through the lower winding ofthe relay SRfof cord C, normalconta'ct 20 of the ringing key RK, ring contacts of the connected plug CP and trunk jack TJ, conductor 19, normal contact 41 of relay LD through the windingof the supervisory relay SR2 of the trunk D', normal contact 61 of the ringing key RK', ring contacts of plug TP and jack J ,-alternate contact 57 of relay CO2, throughthe now closed contacts of the substation switchhook Vat'A E back through alternate-contact 56er relay CO2, the tip contacts of thejack `J and plug TP, normal contact 60 of the key RK", conl i ductor 13, tip contacts of the jack TJ and Vplug CP, normal contact 12 of the ringing key RK of the to ground through upperwinding of the relay SR; -Therelay SR2 energizes over :this circuit and the closing of its alternate contact 70 establishes an energizing circu'it'for the relay 17 traced lfrom battery, Vthrough the winding' ofthe 'relay 17, conductor 25', normal'ontactA 2,6 of relay RR, conductors 27 and V'71, alternate Contact ,f

70 .ofrelay SR2, conductors 72 and' 58`ft0 4 fground'v at alternate contact 59 of 'sleevetrelay vate Vbranch operator associated ,withV the SL?. Relay 17 `upon energi'zation its normal Contact 37 t0 efface the supervisory The supervisory relay SR ofthe cord Cis -now held energized vover the line of the called no' j (ma y.

substation Eand remains energizedv until called subscriber again replaces his receive'n The. closing of ,alternate contact 37 of therelay 17 also establishes an energizing circuit `for the relay 73`traced from battery through the winding of the relay 7 fcondnctor 74","'al' i Vternate Contact 37 of relay'l?, conductm' `58 to v'ground at alternate ContactV 59 -Of` .the

lay SLz. VRelay 73upon energizationcloses itsV alternate contact 7 5 thereby'establsl'lnig ay lockingfcircuit for itself traced 'fronr'atV Y tery through the winding of relay? 3, its'fi "to ground at' alternate contact- 59 efsleeve'm to normal. The calling subscriber at the sublstation A at the main exchange and the called subscriber at the called station E are now in Iconversational circuit the talking circuitl Vbeing traced over the heavily marked conductors.

After the conversation has terminated, the subscribers at the respective substations A and Ereplace their receivers upon their respective switchhooks. The replacing of the receiver at the substation A opens the energizing circuit of the supervisory relay SR of the cord vC and the closing otl its -noi-malconta'ct 7 closesraxcircuit for the answering suf pervisory lamp AS traced from battery through the normal contact 7 .oitl relay SR to ground at alternate contact 7 of sleeve. relay SL. -The replacing ofthe receiver at the private branch exchange substation E opens the energizing circuit of the supervisory relay SR', and theclosiiig oi itsnormal con# tact 9 closes a circuit for the calling supervisory signalV CS to ground at alternate contact 8 of the sleeveV relay SLot the cord C..

`The operator oli' the cord C notingthe two lighted supervisory signals AS and removes the answering plug AP and the calling plug CP from the respective acks J. and TJ thus restoringrespective sleeve relays SLv and SL to eftacethe signals AS and CS and the withdrawal ot the plug Cl) and trunk jack TJ also allows 'cut oil relay CO associat- V'ed with trunk D to restoreto normal.V Y

Vhe'n the called subscriber at the branch exchange substation E replaces '-his receiver Vthe energizing circuit ot thesupervisory re.- lay SR2 is opened at 'the switchhook contactsand the relay SR? restores, closing its normal contact to establish an energizing circuit yttor the link disconnect relay LD oi'thetrunk D traced'irombattery through the winding ot theielay LD, conductor 77, alternate 'contact 78 of the Vrelay 73, conductor 79, alter- )nat-e Contact 8() of the sleeve relay SLZ, conductors 81,82, normal contact 83 of the relay V4t() (which was deenergized as before described)l conductor 84,' normal` contact 7 0 of "the relay SR2, conductors 7 2 and 58 to ground .atalternate contact 59 ot .the sleeve relay SL2.

The deenergizatioii of the relay SR2 also opens the energizing circuit oi the relay 17 at alternate contact 70 andthe relay 17 restoring again closes a circuit toi' the supervisory signal SS of the trunk Dl traced-from battery, through the lamp SS, normal contact 37 oi' relay 17, conductor 58 to4 groundV at alternate contact 59 Vof the sleeve relay SL2.

Y The operator at trunk D notingl the lighted signal SS knows the conversation between subscribers'has terminated and she therefore withdraws the trunk plug TP from the ack *Jef lthe `called substation The," withrelay 7 3 and alsoopens the circuit of the supervisorysignal SS. The apparatus used in Vestablishing a connection from the calling substantion A at theinain exchange ME and the called substation E at the private branch exchange PB is now at-norinaland available for establishing other connections.

Assuming that the substantion in is connected topa private branch board located at a hotel or iii an oiiice andfthat the local subscribers connected thereto are not permitted to make outgoing .calls .without the operators supervision, means are provided in thetrunk eircuitD associated with the private branch switchboard to prevent this unauthorized initiation of calls. This means in the trunk circuit D is so arranged that should the operator at the trunk D be busy handling other calls when-receiving a disconnectsignal from a called substation at the branch exchange and allow the plug Tl? of the-trunk D to remain inthe jack J after receiving theY ldisconnect signal the means in the trunk operates to prevent the-subscriber at the substation E Vfrom initiating Va calland extending theysame to the mainexchange. i

Assuming that the subscriber atrtlie substation E `has I tinished Yconversation and re places his receiver upon theswitchhook and thenj decides to make a call and assuming that the operator is occupied with other business and has notv withdrawn the plug TPtroiii the jack J, thus when the calling?subscriber at 1Ereinoveshis.receiver troni the switchhook the supervisory relayiSlit2 is immediatelv energized. rllhe circuit fot thesupervisory relay SRZ is new traced from batterypthrough the lower winding oi the coil 90, alternate contact 91 'of .the relay LD7 conductor 19 Y through thewiiiding of relay SR2, normal contact'l of the ringing key RK, ring contacts of the coniiected'plug TP and jack l', alternate Contact 57 of thecut eti relav CO2. the closed contacts oit the substation switch; hookbaek through alternateueontact .56 oi thefciit off relay CO2, tipV contacts oit the connected jackil and plug Tl), normal Contact GOotringing key RK conductor'l. alternate contact 92. of relay LD to around through .theupper winding ot theeoil 90. Thei'elay again closes its alternate contact 0 toestablish an energizingcircuit for the relay "17 and the relay upon energization opens itsnormal contact 37 to eiiace supervisory signal SS. Y The relay LD as before described energizes whenthe called subiis scriberreplaces his receiver to open its normal contacts 41 and 46 interrupting the trunk- Vover a circuit which may be traced from bat tery, through the winding of relay LD, conductor 77, alternate rcontact 78 of relay 73, conductor 79, alternate Vcontact 80 of relay SL2, conductor 81, normal contact V93 `of the release key RE, conductor 94, alternate contact 95 of the relay LD, conductors 72 and 58 to ground at alternate contact 59 of the sleeve relay SL?.

The operator of the trunk D seeing vthe supervisory signal SS el'accd knowsV that the subscriber at the substation E is calling and depresses the release key RE which opens the energizing circuit of the relay LD at con`V` tact 93-of the release key'RE and-relay LD deenergizes to again complete its normal con-V tacts 41 and 46 to close the continuity of the trunk conductors 13 and 19V which brings about theenergization of the line relay LR at the main exchange which may be traced from battery through the upper winding of the relay LR, normal contact 10 of ythe cut ofi' relay CO', trunkconductor 13, normal contact 46 of the relay fLD, normal contact ofthe ringing key RK, tip contacts of the trunk plug TPV and'jack J alternate contact 56 of the cut off relay CO2 through Vthe closed contacts at the substation switchhook at E back through alternate contact 57 of the cutv off relay CO2, ring contacts of the jack J and trunk plug TP, normal contact 61 of the ringing key RK', conductor 19,

normal contact 41 Vof .the relay LD, lnormal contact 11 of thecut olf relay CO to ground through the lower winding LR. The relay LR upon energizationcloses its alternate contact 94 and thereby completes a circuit for the line signal S traced from battery through the lamp S to ground at alternate Contact 94 of the line relay LR. The operator associatedv with the cord C noting the lighted signal S inserts an answering plug` AP of the cord- C- into the trunk jack TJ and the,- call from the substation E is taken care of in the usual way. l

y Assuming that the calling plug CP has been withdrawn from the trunk iackTJ associated with the trunk D and that the trunk operator at D has n ot withdrawn the trunk plug TP from the ]ack'J of'a called line, means are provided whereby an operator at the main exchange may insert acalling plug CP into the trunk jack TJ associated with the trunkD and rering VVthe trunk operator without waiting for disconnection of the trunk plug TP from the jack J. vA plug CP having been inserted into the trunk jack TJ the operator associated with'theeonnecte'd cord C now actuates the ringing kev RK to,

connect the ringing'generator G. The ring'- ing current from the generator `Gr maybe traced from the ungrounded pole ofthe gen.-

erator G, alternate contact 12 of ,the ringing,

key RK, the tip contacts of the connected plug CP and trunk jack TJ, trunk conductor 13, conductor 14, condenser ,K,conductor 102v through the upper winding 103 of the ringingl relay RR', conductor 104, alternate Contact 105 of the 'relay LD (which relay was energized when the called subscribed at the substation E replaced his receiver uponA his `switchhook as previously described), conductor 106, trunk conductor 19ring contacts of the jack TJ and plug CP, to ground at alternate contact 20 of the ringing key RK. The relay RR is energizedvand the closing of its alternate contact 107 establishes a locking circuit for itself traced from battery through the lower winding 108 of .the relay RR, alternate contact 107 of relay RR', conductor 109, alternate Contact 78 of relay 73, `conductor 79, alternate contact 80, relay SL2, conductors 81 and 82, Lnormal contact 83 ofrelay .40, conductor 84, normal contact 70 of relay SR2, conductors 72 and 58 to ground at alternate Contact 59'of the sleeve relay SL2. The closin" of alternate contact 110 of relay RR establlshes a circuitfor the callinglamp signal CL, traced from battery through the lamp CL, conductors 24 and 111 to ground at alternate contact 110 of relay RR. The lamp is lighted over this circuit and notifies the operator at the'trunk Dthat a call. from the main exchange is waiting `for attention.

` The operatornow withdraws the trunk plug TP fromthe connected jack J which withdrawal opens the seriesfenergizing circuit of the sleeve relay SL2 of the trunk D and the Y cutoff relay C02 .0f line circuit L. The relay SL2 upon deenergization opens its alternate contact L80 which brings about thedeenerizationof the disconnect relay LD.y The opening of alternate contact 590i relay, SLz brings about the deenergization of the relay 73 and ythe opening of alternate Contact 80" the operation of the circuit from this point i on is the same as previously described.

.I have illustrated and described a certain circuit arrangement but I do not wish to be limited tothe same as changes and modifications Inay readily suggest themselves to those skilled in the art and I therefore'aim tocover all such changes and modificationsas come within the spirit and scope of the appended claims.

Having described my invention what I claim as new and desire to secure by Letters Patent of the United States is Y l.'A telephone system including a calling said trunk circuit controlled by-said called subscriber for disconnecting one end or said trunk circuit from theother end thereof, saidl disconnecting means preventing the eXtenf sion of a recall from said called line to said cord circuit prior to said disconnection, and

means in said trunk to permit the re-ringing of said trunk prior to the disconnection of said trunk from said called subscribers line. e

'2. A'telephonesystem including a calling subscribers line.l and a lcalled'subscribers line, a cord circuit and a trunk circuit for interconnecting said lines, disconnect means in said trunk controlled by said called subscriber for disconnecting one end of said trunk from the other end thereof, said disconnectingmeans preventing the extension of a recall from said called line to said cord circuit prior to said disconnection, and means in saidtrunk controlled by said disconnect means to permit the re`-ringing of said trunk prior to the disconnection of said'trunk from the said called subscribers line.

3. A telephone'system including a calling subscribers line and a called subscribers line, a cord circuit and a trunk circuit for interconnecting said lines, disconnect means in said trunk controlled by said called subscriber for disconnecting'one end ot said trunk from the otherend thereof,- said disconnecting means preventing the extension of a recall from said called line to said cord circuit prior toA said disconnection, a callingV signal in saidvtruiik` and means in said trunk controlled by said disconnect means to permit the operation 'of `the said calling signal in said trunk prior to the disconnection of said trunk from ,said called subscribers line. Y

4. A telephone system including aycalling subscribers line and a called subscribers line, a cord circuit and a trunk circuit for interconnecting said lines, Ldisconnect means in said trunk circuit controlled by said called subscriber for disconnecting one end of said trunk circuit from the other end thereof, and means in said trunk circuit to re-signal the operator of said trunk prior to the disconnection of said trunk from said called subscribers line, said disconnect means preventing the extension of a recall from said called line to said cord disconnection.

5. A telephone system including a calling circuit prior to said subscriber-fs line and Va called subscribers line, a cord circuit and a trunk circuit for interconnecting said lines, disconnect means in said trunk circuit controlled by said called subscriber and operated upon the termination of conversation to disconnect one end of said trunk from the Vother end thereof, and means in said trunk circuit for re-signaling the operator of said'trunk rior to the disconnection of said trunk from said called subscribers line, said disconnect means preventing the extension of a recall from said calledvline to said cord circuit prior to said disconnection;

6. A telephone system including a calling subscribers line and a called subscribers line, a cord circuit and trunk circuit for interconnecting said lines, a link disconnect-relay in said. trunk circuit controlled by said called subscriber and operated upon the ktermina tion of conversation to disconnect one end of said trunk from the other end thereof, and means in said. trunk controlled by switching contacts of saidlinkdisconnect relay to permit the cord circuit operator to re-ring the trunk operator prior tothe disconnection of said trunk from said called'subscribers line, said link disconnect relay preventing the extension of a recall from said called line to said cord circuit prior to said disconnection.

7 A telephoner system including a calling subscribers line and acalled subs'cribers line, a cord circuit and a trunk circuit for interconnecting said lines, a link disconnect relay in said trunk for disconnecting one end of said trunk from the other end thereof, a calling signal in said trunk, and means in said trunk controlled by said link disconnect relay to permit thek cord circuit loperator to re-ring the trunk operator and light said calling signal prior to the disconnection'of said trunk from said called subscribersline, said link disconnect relay preventing the'eXtension of a recall from said called line to said cord circuit prior to said disconnection. Y

8. A telephone lsystem including fa calling subscribers line and a called subscribers line, a cord circuit and a trunk circuit. for interconnecting saidlines, a link disconnect relay inl said trunk lfor disconnecting one end of said trunkfromrthe other endthereof'controllable by'V said called subscriber upon the termination of conversation, a ringing relay 'for said trunk operated byringing current appliedby the cordv circuit operator through contacts of said link disconnect relay prior to the disconnection of said trunk yfrom the called subscribers line,'said linkV disconnect relay preventing the extension of a recall from saidcalled line to said cord circuit prior to said disconnection. v 9. A telephone system including-a calling subscribers line and a called subscribers line, a cord circuit and a Ytrunk circuit for interconnecting said lines, a link disconnect relay in said trunk for disconnecting one end of said trunk from the other end thereof and controllable by said called subscriber upon the termination of conversation, a calling signal for said trunk circuit, and a ringing relay flor said trunk operated by ringing current applied by the cord circuit operator through contacts of said link disconnect relay to light said calling signal to re-signal said trunk operator prior to the disconnection of said trunk from the called subscribers line, said link disconnect relay preventing the extension of a recall from said called line to said cord circuit prior to said disconnection.

10. A telephone system including a cord circuit and a trunk circuit for connecting a calling subscribers line to a called subscribers line, disconnect means controlled by the called subscriber for disconnecting his line from the said cord circuit, said disconnecting means preventing the extension of a recall from said called line to said cord circuit prior to the disconnection of said trunk circuit from said called line, and trunk signalling means operable forthe first exchange subsequent to an operation of said disconnect means.

Signed at Chicago in the county of Cook and State of Illinois, this 27th day of May, 1926.

MICHAEL B. STAZAK. 

